1. Field of the Invention
The present invention relates to a device and a method for separating semiconductor fragments.
2. The Prior Art
Numerous semiconductor materials have to be comminuted for the melting operation in the crucible. In this case, it is imperative that no contamination and fine dust enter the crucible together with the semiconductor fragments. The contamination may reside within the bulk of the material or on its surface. Previously, contamination on the surface, such as contamination formed by the crushing operation or by the previous screening, sifting and separation methods, has been removed in water baths or in acid baths. The drawback of these cleaning methods is the low efficiency and the high costs of using acid. The use of acid is not generally able to remove the extremely undesirable abraded plastic material from the edges of the crusher bars.
Due to the constant contact between materials and the permanent load on the screen material, screening of the polysilicon, for example, by means of a dry screen leads to contamination, abrasion and fine dust which are reflected as problems in the product quality. In addition, the irregular shape of the polycrystalline silicon powder quickly results in blockage of the apertures, e.g. of the gaps in a bar screen or the apertures in a perforated screen.
Wet separation also fails to allow powder sizes to be controlled accurately and reproducibly. This is because the adhesion forces cause the small pieces to adhere to one another and, in particular, to adhere to larger fragments. This presents difficulties not only for controlling the powder sizes but also for discharging the material.
The opto-electrical separation method is also currently unsuitable for delivering the fine powder and dust (max. fragment sizes less than 2 cm). This is because digital measuring technology is not yet able to handle particle streams of greater than 6000 pieces/second of the dimensions indicated above.